1. Field of the Invention
The present invention relates to a portable terminal device and more specifically to a portable terminal device designed to appropriately control an operating frequency of a CPU.
2. Related Art
In recent years, portable terminal devices driven with an internal battery, which are typified by a cellular phone, have been often used away from home or in the motion. In addition, the portable terminal devices are equipped with a function of reproducing video data or music data and a function of viewing/recording one-segment broadcasting data as well as a voice communication function and an e-mail function to enhance their functions.
Along with such a tendency toward an enhanced portable terminal device, a high performance is required of a processor. However, the high-performance processor consumes a lot of power, resulting in a problem of shortening an internal battery life.
To overcome such problem, one known electronic device controls an operating frequency of a CPU and a power supply voltage in a simple manner to enable a power-saving effect (see Japanese Unexamined Patent Application Publication No. 2008-77563 (Patent Publication 1), for instance).
A technique of controlling an operating frequency of a CPU disclosed in the Patent Publication determines an operating frequency according to CPU utilization and thus can appropriately reduce power consumption by suppressing unintended increase of an operating frequency.
However, this technique provides a problem that the determined operating frequency might lead to an insufficient throughput for some processing executed on the CPU and cause user's dissatisfaction at responsiveness and operability of the entire portable terminal device.